Delhiites on Monday woke up to a thick blanket of hazy dust with the air remaining toxic two days ahead of Diwali and the weather office warning of worse air quality days ahead.

Though Sunday was the cleanest November day and an official of the central pollution control agency said the city’s air quality could be relatively better this Diwali due to weather conditions and last month’s Supreme Court order allowing the sale and use of only “green” and “low emission” firecrackers in the National Capital Region (NCR), the reprieve may be temporary.

The weather office has warned of a dip in air quality in the coming days with the northwesterly winds likely to bring pollutants in Delhi’s air from Punjab and Haryana, where farm fires are continuing though the numbers of such cases are seeing a gradual decline.

Burning of crop stubble in these states is considered as one of the reasons behind Delhi’s toxic air quality at this time of the year. Residents of Delhi and the National Capital Region (NCR) have been advised to avoid all outdoor activities, keep medicines handy in case of respiratory diseases and curb use of private cars and two-wheelers.

Exposure to toxic air kills hundreds of thousands of children every year, the WHO said in an October report with doctors saying it is like a ‘death sentence’ for those ailing with lung or breathing disorders.

Srinivas K. Gopinath, a thoracic surgeon at Sir Ganga Ram hospital in Delhi, who recently surgically removed a diseased lung of a 29-year-old, said: “Delhi air is like a death sentence for him.”

Gopinath fears for his patient, who survived tuberculosis but is now at the mercy of another invisible killer — air pollution.

While short-term exposure to pollutants causes airway and lung infections and aggravates breathing disorders, chronic exposure can lead to several life-threatening diseases. “Pollution kills. Every year thousands die of pollution-related ailments in Delhi and NCR during the winters when the air is extremely foul. Pollution is a silent killer; it does not directly kill anyone but aggravates existing diseases,” said Dr Randeep Guleria, director of All India Institute of Medical Sciences (AIIMS).

As cooler air traps pollutants close to the ground, Delhi’s levels of PM2.5 — particles so tiny they can enter the lungs and bloodstream — often soar to beyond 30 times the safe limit.

On Monday, the overall Air Quality Index (AQI) of Delhi was recorded at 342, which falls in the “very poor” category, according to data of System of Air Quality and Weather Forecasting And Research (SAFAR).

Officials say the haze will continue to persist during the early mornings and late evenings for the next few days.

An AQI between 0-50 is considered good, 51-100 is satisfactory, 101-200 moderate, 201-300 poor, 301-400 very poor and 401-500 is marked as severe/hazardous.

With pollution levels in plummeting, several schools in Delhi-NCR have started taking precautionary measures such as suspending morning assemblies and restricting outdoor activities for their students.

Though the Delhi administration is yet to issue an advisory for schools, several government and private schools have started taking initiatives on their own.